ABB Distribution Protection Unit 1500R
1-6
Protective Functions
9/99
website:www.abb.com/papd
Ground Instantaneous Overcurrent Element 50N-2 (IN>>2) - Level 2, Mid set
The 50N-2 function operates when the level of ground current exceeds the pickup level. 50N-2 is used to establish one
more layer of instantaneous overcurrent protection such as a high set instantaneous overcurrent element. If the fault
current exceeds the 50N-2 setting, a
typical scenario would be to trip faster
than the 50N-1 setting, lockout
reclosing, or operate an external lockout
relay. To operate an external lockout
relay with the 50N-2 only, a
programmable output contact must be
mapped to operate on the 50N-2
element only. See the “Programmable
I/O” Section for more details. The
pickup level of 50N-2 is set as a
multiple of the 51N pickup. The timing of the 50N-2 is set strictly as definite time (see Table 1-7). The 50N-2 pickup and
time delay are all set in the Primary, Alternate 1, and Alternate 2 settings groups. For the 50N-2 element to operate the
“Trip” contact, it must be selected in the “Master Trip Output” mapping (see Programmable Trip Contact Section). 50N-
2 is set by factory default to operate the “Trip” contact.
50N-2 tripping can be enabled or disabled in each step of the reclose sequence. See “Reclosing” later in this section for
more details. It can also be supervised (torque controlled) by mapping the “GRD” logical input to a physical input for
external supervision or Logical Output for internal supervision. See the “Programmable I/O” Section for programming
instructions.
Sensitive Earth Fault (SEF) Option, 50N-2 (IO/
>2) - Definite Time
The Sensitive Earth Fault (SEF) is applicable to systems where all loads are connected line to line and no neutral or
earth current flows unless an earth fault occurs. (This options is not applicable to 4 wire multigrounded systems.) This
feature is included on special SEF DPU1500R models only (see Section 12) and replaces the standard 50N-2 element
described earlier. For SEF models a separate SEF current input is provided at Sensor 5 (I
0
SEF). This input can be
connected residually in series with the standard earth fault CT or it may be connected to a separate window type CT
that encloses all three phase conductors. See Table 1-8 for applicable SEF settings.
The analog and digital filtering provide a rejection ratio of third harmonic greater than 50:1 to prevent incorrect operation
due to the effects of distribution transformer excitation currents.
For loop schemes or ungrounded systems, a directional SEF model is available (see Section 12). The directional unit
is polarized, by a separate V
0
(zero sequence voltage) input (see Figure 9-6). The potential transformers should be
connected wye-broken delta. The minimum
polarization voltage is 2 volts and the torque
angle is set 0 to 355 degrees in 5 degree steps
with a sector width of 180 degrees. (Contact
factory for availability of 1-volt sensitivity). The
SEF 50N-2 tripping can be enabled or disabled
in each step of the reclose sequence. See
“Reclosing” later in this section for more details.
It can also be supervised (torque controlled) by
mapping the “SEF” logical input to a physical
input for external supervision or Logical Output for internal supervision. See the “Programmable I/O” Section for
programming instructions.
Table 1-8. 50N-2 (IN>>2) Sensitive Earth Fault Units
The SEF 50N-2 is disabled in the factory default settings.
SEF 50N-2 Parameter
Range/Curve
Increment
Pickup
0.005 to 0.200 ampere 0.0005A
Definite Time
0.5 to 180 seconds
0.1 seconds
The 50N-2 element is disabled in the factory default settings.
50N-2 Parameter
Range/Curve
Increment
Pickup
0.5 to 20 x 51N setting
0.1x
Definite Time
0 to 9.99 seconds
0.01 sec.
Table 1-7. 50N-2 (IN>>2) Characteristics
